One such adaptation is the closer proximity of the terrestrial snake's heart to its head which helps to ensure circulation to the brain regardless of the snake's orientation in space the heart of sea snakes can be located near the middle of the body a position that minimizes the work entailed in circulating blood to both extremities in arboreal snakes however which dwell in trees and often assume a vertical posture the average distance from the heart to the head can be as little as 15 percent of overall body lenght such a location requires blood circulated to the tail of the snake travel a greater distance back to the heart a problem solved by another adaptation when climbing arboreal snakes often pause momentarily to wiggle their bodies causing waves of muscle contraction that advance from the lower torso to the head by compressing the veins and forcing blood forward these contractions apparently improve the flow of venous blood returning to the heart